1. Field of the Invention
This invention relates generally to the field of gaseous fuel carburetion. More specifically, the invention relates to a low-Btu gas carburetion system and method for use with a consumer such as an engine generator that may be operated intermittently.
2. Background of the Invention
The production of energy is critical to the economic survival of developed nations. The use of recoverable sources of energy provides advantages to process industries in terms of efficiency and economy and may decrease negative environmental impact. Successful utilization of low-Btu gases for fuel may provide such advantages. Low-Btu gases include, among others, biogas or digester gas, landfill gas, associated oil well gas, and manufactured gases from either fossil fuels or biomass gasification.
Existing methods of providing gaseous fuels to engine generator systems are limited to gases having heating values of 500 Btu/scf and greater. These methods are not feasible with low-Btu fuels. Although fuel injection systems have been disclosed for low-Btu gas control, the development of pressure-based carburetion methods for low-Btu gas has not been successful. Commercial carburetion for high-Btu fuels includes diaphragm and venturi mixers for control of the air-to-fuel ratio. In high-Btu carburetion, air is typically naturally aspirated, and fuel is supplied by a zero-pressure regulator The zero-pressure regulator maintains a consistent pressure differential between the air and fuel supply to the carburetor, which may be important for proper mixing within the carburetor geometry. High-Btu carburetors for fuels such as natural gas operate at volumetric air-to-fuel ratios of 10:1, where the heating value of the fuel is 1000 Btu/scf. In contrast, a typical low-Btu fuel requires an air-to-fuel ratio of 1:1, where the heating value of the fuel is 100 Btu/scf. The significant volume of additional gas to be mixed with air in a low-Btu carburetor cannot be addressed with high-Btu geometry carburetors. Additionally, while high-Btu fuel is typically supplied from a gas source that may be intermittently supplied, low-Btu fuel is typically supplied continuously from a source such as, for example, a gasifier. Gas sources such as gasifiers are generally operated continuously to maintain proper reactor temperature and consistent gas quality. It is undesirable and impracticable to interrupt the continuous production of gas. A need exists, therefore, for a means to couple a continuous source of low-Btu gas to a consumer such as an engine generator that may be operated intermittently and to provide the proper air-to-fuel ratio to the consumer.
Methods for adapting low-Btu gas (producer gas, biomass gas, or syngas) to engine generator systems have remained limited to manual valve mixing or electronic control. The integration of an engine generator with a continuous source of low-Btu gas has not previously been demonstrated in the art.
U.S. Pat. No. 4,278,064 by Regueiro describes a fuel control system for a dually fueled power unit. The patent discloses a gasifier coupled to a diesel engine with electronically controlled valves specific for load control. The object of the invention is to control the dual fueling of the engine by electronic fuel injection and does not address traditional pressure-based carburetion.
U.S. Pat. No. 5,070,851 by Janisch discloses a traditional pressure-based air-gas mixer or carburetor intended for low-Btu gas specific to Briggs and Stratton engines, which are typical small engines used for lawnmowers and other small engine applications. The object of the invention is to supplement gasoline fuel. Janisch does not address large natural gas or diesel engine generation sets and the means by which large engine generators can be supplied low-Btu gas at the correct air-to-fuel ratio. Janisch does not address a means for coupling a continuous gas supply to an intermittent consumer via a gas outlet.
Other methods of introducing gas to piston engines include fumigation. U.S. Pat. No. 4,694,802 by Lowi refers to previous fumigation efforts and describes a means comprising variable area venturi. Lowi does not address the application of low-Btu gas or the application of a gas outlet device for coupling a continuous gas supply to an intermittent consumer.
U.S. Pat. No. 5,895,507 by Southards describes a diesel engine coupled to a black liquor gasification process. Specifics regarding the coupling of the process to the diesel engine are not claimed. King et al. in U.S. Pat. No. 5,724,948 reveals a method for applying biogas to an internal combustion engine. King et al. employs a standard gaseous carburetor for fuels having heating values above 500 Btu/scf and does not address the challenges concerning the implementation of low-Btu fuels. Vinyard in U.S. Pat. No. 6,805,107 provides a method for dual-fuel operation of an engine utilizing syngas and propane. Vinyard does not address pressure-based air-gas mixing or carburetion, but rather discloses electronic control.
Accordingly, there is an ongoing need for a carburetion system and method for supplying low-Btu gas at the proper volumetric air-to-gas ratio from a continuous gas source to a consumer such as an engine generator that may be intermittently operated and to which the continuous gas source may be permanently coupled.